Monday, November 13, 2006
117-15
Comparison of Vented Chamber Greenhouse Gas Sampling Techniques Including and Excluding Vegetation.
R. S. Tubbs and J. S. Schepers. USDA-ARS, 3043 Fletcher Ave. Apt. 233, Lincoln, NE 68504, United States of America
Determining the most appropriate method of sampling greenhouse gas fluxes is no simple task. Vented chambers are the most common technique because they are economical and practical to deploy. This experiment took place in a seed corn field in Shelton, Nebraska to evaluate fluxes of CO2 and N2O utilizing different chamber deployment strategies. Samples were taken between rows (excluding plants), centered on the row (including plants), centered on the row (cutting the plants out of the sampling area), and from bare soil. The plots including plants in the chamber had much higher CO2 values (regularly above 100 kg CO2-C ha-1 d-1) than the treatments excluding plants, as expected. The fluxes between rows were usually less than 30 kg CO2-C ha-1 d-1 and equal to the emissions from the bare soil treatment except when taken shortly after a rainfall or irrigation event (bare soil would exceed 40 kg CO2-C ha-1 d-1). Nitrous oxide emissions had little variation over the course of the growing season among these sampling methods, except when following an irrigation event (25 July 2005). At that time, emissions exceeded 100 g N2O-N ha-1 d-1 from bare soil, compared to 33 g N2O-N ha-1 d-1 with plants and less than 5 g N2O-N ha-1 d-1 after cutting and between rows. Soil microbial activity endured longer in bare soil since the soil remained wet for a longer time period compared to the plots that had plants. These results show that including plants inside the chamber can greatly effect CO2 emissions, but has little effect on N2O emissions unless the soil is saturated. The data also allows the estimation of the amount of CO2 and N2O being emitted from the plant compared to that which is coming off the soil.
Handout (.pdf format, 149.0 kb)